In a digital still camera using a solid-state image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor), a lens system having a comparatively long back focus is necessary in order that a member such as an optical low-pass filter should be arranged between the rearmost part of the lens element and the solid-state image sensor. Further, in the shooting optical system of the digital still camera, a satisfactory telecentric property is required in order to avoid shading that could cause a reduction in the amount of light in the periphery on the image surface.
A large number of types of digital still cameras can be considered. One of these types is a compact type. As zoom lens systems suitable for digital still cameras of compact type, in the prior art, three-unit zoom lens systems have been proposed that, in order from the object side, comprise a first lens unit having negative optical power, a second lens unit having positive optical power and a third lens unit having positive optical power. The inventors of the present application have proposed a three-unit zoom lens system appropriate for a digital still camera of compact type (Patent Document 1).
[Patent document 1] International Publication No. 03/085440 Pamphlet